A genetic disorder associated with variation(s) in the AP4 genes: AP4B1, AP4E1, AP4M1, and AP4S1. The phenotypes observed in individuals with genetic variants in these genes are often complex and include intellectual disability, spastic paraplegia, microcephaly, brain abnormalities, and seizures. The disease is AP-4 deficiency syndrome (MONDO_0100176, a Monarch Disease Ontology term).